I remember seeing this show 4-5 years ago.
It was about a boy, in the process of saving his grandfather or someone, who goes into a library regularly and gets transported to another world, where he fights monsters along with a boy and a girl. After defeating the monsters, the boy captures them using a torch like thing and puts them into a book.
Is this Matt Hatter Chronicles (2011-2015)...?
Matt Hatter is an ordinary child who discovers that the monsters of his family's horror movies are alive in another dimension called "the Multiverse", controlled by the nefarious Lord Tenoroc. This dimension can only be accessed through the Notting Hill Coronet, his family's movie theater. With his grandfather Alfred trapped inside the Multiverse, Matt, along with his new friends Roxie and Gomez, must capture the movie monsters, save Alfred, and restore peace to the Multiverse.
The main character, Matt Hatter, moves from the US to London with his parents and discovers that a screen in his grandfather's, movie theatre is a portal to the 'Multiverse,' another dimension made up of twelve realms.
At the start of each episode, the main antagonist of the show, Lord Tenoroc, releases a horror movie villain/monster from hexagonal discs called Life Cells, to achieve some sinister objective or other within the Multiverse.
It used to be the job of Matt's grandfather to capture these villains/monsters, with the assistance of Roxie and Gomez, a pair of kids from the Multiverse, but his grandfather has been trapped by Tenoroc, so now Matt has to take over.
When each villain/monster is critically harmed in some way, they "go hologram," at which point Matt can use a handheld device called a Cell Blaster to absorb and contain them, a bit like a Ghostbuster's trap.
He then plugs the Cell Blaster into the front cover of the Chronicles, a special book containing the Villain Vault, a prison pictured on a page within the book.
Shortly after Matt captures and imprisons a movie villain, the 'Black Knight,' near the end of the first episode, it's indicated that each time he does this, it makes Tenoroc weaker and his grandfather stronger.
Matt first learns of this stuff when he picks the Chronicles up from a bookshelf in his grandfather's theatre and discovers a secret passage behind the bookshelf, as well as a recorded message left for him by his grandfather.
You can view the scene with the bookshelf at around the 3:38 mark in the video below, and you can view the scene of him capturing the Black Knight at around the 18:56 mark.
